Monte Carlo calculations have been carried out for the sputtering energy reflection coefficient (YE) of plasma ions incident on a carbon surface. The calculations incorporate a simulation of the velocity distribution of plasma ions incident on a surface with a floating potential. The average energy of an ion can increase by more than a factor of three as a result of this potential and the effect onYEcan be significant. An analytic form forYEis constructed expressed in terms of the ion plasma temperature and the surface floating potential. The new model provides a fast and accurate means to calcualteYE.